Process of carburizing steel and iron



Patented 'Jan. 8, 1924.

UNITED STA I OFFICE.

TOYOHCHIBO TASHIBO, 0F TOKYO, JAPAN.

PROCESS OF CARBUBIZING STEEL AND IRON.

" Drawing.

To all whom z'tmay condom:

Be it known that I Toroxronmo TA- srrmo, subject of the mperor of Ja an,residin at No. 450 Shirokane Sankoho, Shiba u, Tok 0, Japan, haveinvented new and useful mprovements in a Process of Carburizing Steeland Iron (for which I have filed application in Japan August 13, 1918,application No. 40,345), of which the following is a specification. g

This invention relates to improvements in the process of carburizinwrought iron, steel or steel alloy, or artic es made thereof, andconsists in causing carbon monoxide to form in a carburizing chamberwhich can be tightly closed and making it toiact in its nascent stateand under pressure on the 'ma-' terial to be carburized. The object ofthis invention is to cause carbon by a simple means to impregnate .deepand in a short time, utilizing reaction heat and pressure.

There are known several carburizing processes, but these may be classedinto two.

In the first class, which is characterized by the use of solid carbon'ving materials, material rich in carbon, sutii as charcoal or the like,or a cyanide, or charcoal mixed with an oxidizing agent, is used, andcarbon monoxide is produced. However, in all these processes, althoughmeans are taken to preventthe combustion gases entering the carburizingchamber, no attempt: has been made to intercept, at least withintention, gases generated in the carburizing chamber and retain themthere, thus increasing pres sure therein, such gases being rather made.nor any usefulgas 1s generate to escape rapidly therefrom.

In the second class, carbon containing gas such as a hydrocarbon,cyanogen, carbon monoxide or the like is burizing chamber, and the ironor steel material is made to take carbon therefrom. Sometimes, charcoal=or the like is put in the carburizing chamber and carburlzing gasmentioned above is forced thereinto, but no oxidizing action takes placebetween the gas and the charcoal.

Again in processes of the first class, carbon monoxide is formed in thecarburizing chamber, but it has not much tendencyto penetrate into thematerial under treatment, and after remaining in contact therewith for ashort time, it escapes there rom, Thus large gas containing carbon isused forced into the car Application fled. Kay 24, 1921. Serial No.472,282;

the waste of that fias is very great and the effect is very smaMoreover, in the ,carburizing chamber oxidizin takes (place andconsequent y reaction heat is pro need; but as the esca ing gas carriesout that heat, as much heat is lost as is produced, and the temperatureof the chamber 1s never raised by such reaction heat. Thus,

a large quantity of expensive carbu agent is spent but the efi'ect isvery slight. According to experiments thus far known, iron was subjectedfor eight hours to a temperature of 2000 F., using as carbon givinmaterial charcoal mixed with 40% o barium carbonate, and the result wasthat the material was carburized to a depth of 0.177 inches; and theresult obtained by the same process using only charcoal powder withoutmixing barium carbonate therewith was impregnatlon of carbon to adept-hof 0.138 inches. Notwithstanding the use of a amount of bariumcarbonate, the result was that the iron was carburlzed 1.28 times deeperthan when only carbon without any oxidizing agent is used. No wonder,therefore, that in lar lfactories where armour plates are manu a ctured,there are still many. which use only carbon powder for carburizing pure.

In the secon class process, a compound for 'ving carbon to the iron. .Orsometimes solid carbon is also kept in the carbu. chamber, but this isuseful only for deoxidizing purpose, and no oxidizing action takes placeetween the. same and the carbon' givin gas,

onsequently, presence or non-presence of solid carbon has no directeffect on carburizing. Moreover, notwithstanding that it is a verydiflicult task to maintain a pressure of from two to four atmospheres ina high temperature of not less than 900 (3., according to this processwrought iron 22 mm. thick must be subjected to such a heat under such apressure for forty hours.

' My invention is an improvement in the above described processes, andconsists in fillinga carburiz-ing chamber, so constructed as to betightly closed, with iron material and carbonaceous substances, and incausing carbon monoxide to form in the carburizmg chamber, and to act inits nascent action briskly.

state upon theiron material under a presas carbon giving material andoxidizingagent charcoal powder mixed with 25% of mixture of equal partsof iron oxide and manganese peroxide, subject the whole toheat atbetween 800 and 950 C. for two hours and a half, maintaining thepressure within the carburizing chamber higher than the atmosphericpressure by 0.153 pound per one square inch.

The result will be the carburization of the iron pieces to a depth of0.5 inches or 13 mm. Even the central part will be found partiallyconverted into steel, points having steel lustre being foundinterspersed there.

Ewample 2.-Take iron pieces one inch thick, and subject it to thetreatment described in Example 1. Then embed the iron pieces thustreated in a mixture of equal parts Example 3.-Take iron pieces 1.2.inches,

or 32 mm., thick of the kind above mentioned, and subject them first tothe second treatment described in Example 2; Then, repeat the sametreatment but subjecting the iron pieces to a heat above 950 C. and fora longer time, Thus the time during which the iron pieces are subjectedto efiicientheat, is five hours and a half. A

Then the iron pieces will be converted into a high carbon steel, smallblisters being formed on the surface and a small part of the surfacebeginning to melt.

use is Japanese knife iron,

of mixture of carbon giving material and oxidizing agent, once used in,

the atmospheric that is for three hours.

ineoeeo In this invention any low grade oxide, or I ore, which freesoxygen at a high temperature and does not contain any injuriousingredient such as sulphur, phosphorus, or the like, may be used aoxidizing agent instead of iron oxide and manganese peroxide. Or,oxidizing agents such as air, oxygen or the like may be introduced fromoutside. Moreover, carburization may be accelerated by increasing thepressure an temperature, but in this case, a great care must be taken,as the material under treatment will be converted into high carbonsteel, and begin to melt, and the treatment will go beyond the limit ofcarburization. To give a few examples, iron pieces 1.2 inches thick, 1.4inches broad and 1.6 inches long of the kind of knife steel abovementioned, together with a mixture of charcoal powder with 20% ofmanganese peroxide, were subjected to a heat not higher than 1200 C. forthree hours at a pressure higher than the atmospheric pressure by 0.3pound per square inch; and the pieces were found wholly converted into ahigh 'carbon steel and in a half melting condition, a part actuallyflowing and the pieces being found somewhat changed in its shape. Again,rod one inch square of the same kind of iron were subjected togetherwith charcoal powder mixed with 10% of manganese peroxide to thesameheat as in the above example for two hours and a half at a pressurehigher than the atmospheric pressure by 1 pound per square inch and theiron rods melted and were converted to grey pig iron. Tron pieces 1.5inches thick, 2 inches wide and 2.5 inches long, being heated in a hightemperature furnace together with a mixture of 20 parts of manganeseperoxide, and 80 parts of charcoal or one hour forty minutes at apressure higher than the atmospheric pressure by rods of half an inchsquare, they were perfectly converted into steel after such treatment ofone hour. In all the above experiments, cast iron pieces placed incontact with walls of the carburizing chamber for the purpose ofadjusting pressure were never melted although they were used severaltimes. This shows that notwithstanding the furnace temperature did notrise to 1220"" (l, the temperature at which grey cast iron melts. thetemperature in the interior 'must have been raised by reaction to morethan Ill) 142O C., the temperature at which highcarbon steel melts. I

According to my invention, charcoal iron can be carburized in two hoursand a half to a depth from 10 to 13 millimeters, and a piece 26millimeters thick of the same iron can be wholly converted into steel infive hours, giving to the material the mild carburizing treatment. Usingthe mild and medium carburizing treatments consecutively on a piece ofcharcoal iron 26 millimeters thick, it can be wholly converted'intohigh-carbon steel in five hours and a half, and if the high carburizingtreatment be given to the same piece, the same result can be obtained inone-half or onethird of that time. Thus the time required to carburizeiron using only charcoal powder as hitherto practiced, can be reduced toone hundredth o'r one-two hundredth, and

j the same result as obtained by the process explained above under class2, can be secured in one tenth or one twentieth of the time required inthat process.

The characteristics of the products obiained by my invention are, (1)material .s carburized uniformly, carbon impregnating with comparativelygreater uniformity even into the deepest part; (2) from the nature ofthe invention, the effective gas within the carburizing chamber actsupon the material to be carburized' with equal tension all over itssurfaces, and consequently the product is most suited as materlal formanufacturing crucible steel; and (3) as material can be carburizedwithout producing any blister on the surface, my process is best suitedfor carburizing iron ware.

I claim 1. The process of carburizing iron, steel and the like, whichconsistsin embeddin the material to be carburized in a bed of a mixtureof carboniferous substance and metallic peroxide in a carburizingchamber that can be tightly closed, and causing carbon monoxide to actin its nascent state under a pressure higher than the atmosphericpressure by heating, utilizingthe reaction heat produced when the saidcarbon monoxide is formed.

2. The process of carburizing iron, steel and the like, which'consistsin placin the material in a carburizing chamber,'m1'xing a carbon givingmaterial with iron oxide and manganese peroxide, subjecting the wholesto a heat at a temperature between the approximate limits of 800 and950C. and maintaining the pressure within the carburizing chamber higherthan the atmospheric pressure.

3. The process of carburizing iron, steel manganese peroxide inproportions of apcharcoal powder with iron oxide and manganese peroxide,subjecting the whole to heat at a temperature between the approximatelimits of 800 and 950 C. and maintaining the pressure within thecarburizing chamber higher than the atmospheric pressure. i

5. The process of carburizing iron, steel and the like, which consistsin placing the material in a carburizin chamber, mixing charcoal powder,iron oxide and manganese peroxide in proportions of approximately 75 percent, 12% per cent and 12% per cent respectively, subjecting the wholeto heat at a temperature between the approximate limits of 800 and 950C; for a period of about 5% hours, and maintaining the pressure withinthe carburizing chamber higher than the atmospheric pressure byapproximately 0.153 pound per square inch.

6. The process of carburizing iron, steel andthe like, which consists inplacing the material in a carburizing chamber, mixing a carbon givingmaterial, 1ron oxide and manganese peroxide in proportions ofapproximately 75 per cent, 12% per cent and 12% per cent respectively,subjecting the whole to heat at a temperature between the approximatelimits of 800 and 950 for a period of about 2 hours, and maintaining thepressure within the carburizing chamber higher than the atmosphericpressure by approximately 0.153 pound per square inch, then embeddingthe material in a mixture of equal parts of carbon giving material andoxidizing agent mixed with about 20 per cent of lIOIl oxide, subjectingthe whole to heat at a temperature between the approximate limits of 800and 950 C. for a further period of approximately 2%; hours, andmaintaining the pressure within the carburizing chamber higher than theatmospheric square inch.

7. The process of carburizing iron, steel and the like, which consistsin placing the material in a carburizing chamber, embedding the materialin ya mixtureof equal parts of carbon giving material and oxidizingagent mixed with about 20 per cent of iron oxide, then subjecting thewhole to heat at a temperature between the approximate limits of 800 and950 C. for a period of approximately hours, maintaining the 4L 4 ineoaao pressure within the carburizing chamber whole to heat at atemperature in excess of higher than the atmospheric pressure by a 950(3., for a further period of approxiproximately 0.285 pound per squareinc mate-1y 3 hours and maintaining the same 10 then embedding thematerial in a mixture of pressure within the carburizing chamber.

(- equal parts of carbon giving material and In testimony whereof I havesigned my oxidizing agent mixed with about 20 per name to thisspecification.

cent of iron oxide, again subjecting the TO'YUKICHIRQ TASHIRO.

